<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }
    ul {
      list-style: none;
      margin: 50px auto;
      width: 1000px;
      height: 60px;
      background-color: lemonchiffon;
      border-bottom: 1px solid #000;
      /* padding-top: 10px; */
    }

    li {
      height: 50px;
      margin-right: 30px;
      float: left;
      border: solid #000;
      border-width: 1px 1px 0;
      margin-top: 10px;
    }

    a {
      padding: 0 20px;
      display: block;
      height: 100%;
    }

    li:hover {
      margin-top: 0;
      height: 60px;
      background-color: #fff;
    } 
  </style>
</head>
<body>
  <ul>
    <li>
      <a href="#">Index</a>
    </li>
    <li>
      <a href="#">About us</a>
    </li>
    <li>
      <a href="#">Index</a>
    </li>
    <li>
      <a href="#">About us</a>
    </li>
    <li>
      <a href="#">Index</a>
    </li>
  </ul>
</body>
</html>